1. Field of the Invention
The present invention relates to network communication systems and more particularly, to local network interface systems for use in a word processing system.
2. Description of the Prior Art
To allow two or more so-called intelligent terminals to communicate with each other, various communication systems, called networks, have been developed. These networks allow terminals, work stations, or data processing stations to share each other's resources when required. A common communication medium is usually employed over which data can be transferred among the stations.
The communication medium most commonly employed is a coaxial cable, along which a plurality of taps are located. Stations can be connected directly to the coaxial cable via the taps, or stations can be connected to each other via a nodal point or node, which in turn is connected to the coaxial cable via a tap. The tap allows the node to broadcast data to and receive data from all other nodes or to and from individually connected stations on the communication network. Any station on the network may initiate a transmission of data on a free channel of the communication medium.
In many systems, nodes are devices specially designed to transfer data between two data processing stations, between two communications channels or between two branches or segments of a communications channel. Often these nodes are complex special purpose devices, not required for any function other than for transferring information, which tend to make the communications system or network complicated.
Another problem heretofore inherent in networks having separate intelligent data processing stations connected to each other via a communications medium is data handling and the supervision thereof. In many previous systems, a processor, CPU or microprocessor included in each data processing station controls data transfer between its associated station and the communications channel to which it is connected. The supervision of this data transfer function can be time consuming for a processor whose time should be better spent performing other tasks. A system in which a great amount of data is transferred among a number of stations at relatively high speed requires an appreciable amount of processor supervision in the aforementioned systems. Clearly, the greater the amount of data transfer, the more processor time must be consumed in performing this function.